Law enforcement sources tell TMZ ... the incident went down Sunday around 2:45 PM at the YouTube star's L.A. crib. We're told the guy hopped the wall ... and when people inside noticed, they called cops and told officers they are armed and will protect themselves if the trespasser tries getting inside the house.

Check out the video ... before any shootout could erupt, an LAPD helicopter was hovering directly above the house. You can also see the alleged trespasser ... who by then, had already made his way outside with, for some reason, luggage in tow.

He also had his hands raised ... and moments later an LAPD cruiser rolled up and took the guy into custody.